--- transcoders/video_ffmpeg.inc.orig   2011-07-06 13:48:33.000000000 -0400
+++ transcoders/video_ffmpeg.inc        2011-07-06 13:48:47.000000000 -0400
@@ -82,7 +82,8 @@ class video_ffmpeg implements transcoder
         $options = $this->params['cmd_path'] . ' ' . t($this->params['thumb_command'], array('!videofile' => $videofile, '!seek' => $seek, '!thumbfile' => $thumbfile));
         // Generate the thumbnail from the video.
         $command_output = $this->run_command($options);
-        if (!file_exists($thumbfile)) {
+        // don't consider zero-byte files a success
+        if (!file_exists($thumbfile) || filesize($thumbfile) == 0) {
           $error_param = array('%file' => $thumbfile, '%cmd' => $options, '%out' => $command_output);
           $error_msg = t("Error generating thumbnail for video: generated file %file does not exist.<br />Command Executed:<br />%cmd<br />Command Output:<br />%out", $error_param);
           // Log the error message.